Dependent data objects
Dependent maps, tables or columns are the result of a calculation (in which you used the definition sign =) or another operation. The complete expression by which dependent output objects are created is stored by the output maps, tables and columns as the object's definition. Dependent data objects thus know how they were created and on which input data they depend.
Based on the definition, dependent data objects can be made up-to-date in case input objects on which they depend have changed. When the definition of a dependent raster map or a dependent column is a MapCalc or TabCalc formula, you can even change the expression itself.
For dependent maps and tables, the definition is stored in a map's or table's object definition file. In principle, only the object definition file is stored on disk. When a dependent map or table is displayed, the data file is automatically calculated and stored on disk. The definition of a dependent column is stored in the object definition file of the table; dependent columns are always calculated.
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